Field sprayers and spray booms hitched to work machines, such as tractors, in some cases have very large working widths of more than 20 meters. Such wide spray booms are folded and collapsed in for transport purposes. In the field, symmetrical cantilevered arms of several meters length are located on both sides of the work machine, which cantilevered arms have a varying spacing from the ground according to surface conditions and field relief. Since the downward-directed nozzles for spreading a spraying agent, for example, a plant protection agent, which nozzles are arranged on the cantilevered arms, each have a defined spray cone, varying the spacing of the nozzles to the ground results in an uneven covering of the field with spraying agent. In addition, the danger of the spraying agent drifting greatly increases as the distance of the spray nozzles from the ground increases, since even slight air movements negatively affect the finely dispersed drops.
With increasing cantilever dimensions and the associated working width there is therefore a necessity to guide the spray boom at as uniform a spacing from the ground as possible, because minimal inclines of the spray boom will lead to large spacing differences of the nozzles to the ground.
In this context, it is known to suspend a spray boom from a carrier vehicle to be rotatable about at least one axis of rotation about a central pivot point. The rotation or pivot axis in this instance preferably runs parallel to the longitudinal axis of the carrier vehicle. In order to ensure an even spreading of the spraying agent, the spacing between the top surface of the growth and the spray nozzles must be constantly controlled to a defined spacing. On horizontal agricultural fields, this can generally be achieved by self-leveling, in which the spray boom aligns itself in the horizontal plane with the center of gravity of the spray boom being located below the central pivot point and the spray boom being suspended, for instance, to be freely and swingingly rotatable. The desired effect will not occur, however, for agricultural fields running along a slope.
In order to constantly control to a defined spacing the spacing between the top surface of the growth for agricultural fields running in any plane and the spray nozzles arranged on a spray boom pivotably suspended about a central pivot point, it is therefore known to pivot the spray boom, which is, for instance, raised to a desired spacing from the ground, about a pivot axis running through a central pivot point such that the spacing is optimized over the entire working width. For this purpose, an alignment changing torque has to be exerted on the spray boom about a pivot axis running through a central pivot point. This is carried out by means of at least one actuator, which transmits, at least as required, a force or a force couple affecting an alignment changing torque about a pivot axis from the carrier vehicle onto the spray boom in order to change the alignment of the spray boom.
This alignment changing torque accelerates the spray boom in a desired target rotational direction. Without countermeasures, the spray boom would continue to rotate about the pivot axis even after the impact of the alignment changing torque has ended, since the spray boom would retain its angular momentum due to the mass moment of inertia. In order to decelerate the spray boom, a braking torque in opposite to the previous alignment changing torque therefore has to be induced. This braking torque counteracts the rotary movement initiated by the alignment changing torque and thus damps the system of the spray boom, which is rotatably suspended about the central pivot point.
Up to now, mechanical dampers, which are arranged between the carrier vehicle and the spray boom, are usually used for generating the braking torque. If the carrier vehicle, however, rotates about the pivot axis due to bumps, for example, and the spray boom stands still, this will also result in a relative rotation between the carrier vehicle and the spray boom. A mechanical damper arranged between the carrier vehicle and the spray boom would counteract this relative rotation and thus transmit a torque, acting about the pivot axis, to the spray boom, such that a coupling exists between the carrier vehicle and the spray boom.
The coupling likewise exists if a measuring system is used as a basis for controlling the torque, which measuring system measures a relative angle and/or a relative rotation between the carrier vehicle and the spray boom.
In addition, measuring systems are known, which use tilt sensors arranged on the spray boom for determining the position of the spray boom. The angular velocity of the spray boom can be acquired independently of the carrier vehicle from the temporal derivation of the tilt. In the instance of lateral accelerations such as occur, for example, when driving along curves, tilt sensors however provide an incorrect tilt. Therefore, a calculation will also result in an incorrect angular velocity.
A spray boom that has a cantilever, which is put together from segments, is already known from the prior art. DE 32 02 569 A1 thus discloses a distribution machine, in which individual segments are connected to each other and the movement of the individual segments is effected passively. For this mechanism, a supporting element is necessary on the outer side of each of the cantilevers in order to enable the pivoting process. In order to prevent loss of harvest, it is however desirable to achieve an adjustment of the individual segments with regard to different ground contours without being in direct contact with the ground.
DE 18 33 453 U furthermore discloses a spray boom comprising nozzle trees, which are arranged on a cantilever by means of elastic elements. By the elastic elements, the nozzle trees can recover a vertical position even after a pivoting process of the cantilever. According to that document, the cantilever is arranged to be pivotable about only one axis, so that the spray boom possesses only a limited flexibility. Due to the high degree of irregularity of ground structures occurring in practice, spray booms with a greater flexibility are desirable in order to ensure an even distribution of the spray liquid on the soil.
A spreading apparatus for spreading liquid and/or solid active agents is known from DE 10 2007 025 751 A1. The spread apparatus comprises a spreading boom arranged on a self-propelled or towed vehicle, which spreading boom is mounted to be pivotable about a suspension point approximately parallel to a driving direction. The spread boom consists of a middle part and lateral cantilevered arms. The middle part is coupled with a frame section of the vehicle via at least one controllable actuating device. The actuating device induces a defined actuating power and/or a defined actuating torque between the middle part and the frame section for the purpose of pivoting the spreading boom relative to the frame section. Inducement is carried out independently of disturbance torques resulting from vehicle movements.
An automated spreading apparatus for spreading liquid and/or solid active agents, which is also referred to as an accompanying spreading apparatus, is known from FR 2 779 031 A1. The spread apparatus comprises a spreading boom arranged at a self-propelled or towed vehicle, which spreading boom is mounted to be pivotable about a suspension point approximately parallel to a driving direction. The spread boom consists of a middle part and lateral cantilevered arms. The middle part is coupled with a frame section of the vehicle via at least one controllable actuating device. Via at least two points of application, the actuating device induces at least two actuating forces between the middle part and the frame section for the purpose of pivoting the spreading boom within a vertical plane relative to the frame section. Inducement is carried out by overcoming the rotational inertia of the spreading boom and simultaneous reduction of disturbances by movements of its center of gravity. In the process, the center of gravity is shifted transversely to the driving direction within the vertical plane. A regulation causes the spreading boom to follow up. The actuating device can be designed as a screw spindle or as a hydraulic construction, for example.
A spreading apparatus for spreading liquid and/or solid active agents is known from FR 2 270 774 A1. The spread apparatus comprises a spreading boom arranged at a self-propelled or towed vehicle, which spreading boom is mounted to be approximately parallel to a driving direction. The spread boom, consisting of a middle part and lateral cantilevered arms, is connected to a vertical cylinder by means of two pins, with the vertical cylinder being arranged at a suspension point of a frame section to be pivotable about an axis parallel to the driving direction. The opposite end of the vertical cylinder is guided between two horizontal cylinders supporting themselves against the frame section. The vertical cylinder and thus the spread boom can be aligned parallel to the ground by actuating the horizontal cylinder. The spread apparatus provides two operating modes. One operating mode provides aligning the spread boom by a height adjustment of the vertical cylinder and by lateral tilting of the vertical cylinder by means of the horizontal cylinder. Another operating mode provides removing the lower pin in rough terrain such that the spread boom can swing freely.
An ultrasonic sensor controlled height control and position control for a spreading apparatus for spreading liquid and/or solid active agents is known from DE 41 40 254 A1.
The prevention of harmonic couplings in a spreading apparatus for spreading liquid and/or solid active agents is known from WO 2004/041446 A1, in which natural resonant frequencies of the cantilevered arms of a spreading boom, both in an empty state and in a full state of the lines and also during spraying operation, the resonance frequency of a rotary oscillation of the swingingly suspended spreading boom, the resonance frequency of a spring suspension of the vehicle to which the spreading apparatus is fastened, the resonance frequency of active agent sloshing in the tank provided for the agent, and the resonance frequency of an active agent pump are independent of each other. For this purpose, the cantilevered arms can be constructed to be adjustable in length.
Spreading apparatuses for spreading liquid and/or solid active agents are known from EP 0 157 592 A2. A first spreading apparatus provides a freely swinging suspension of a spreading boom with occasional correction processes taking place, in which the height of the spreading boom above the ground is readjusted according to a specified spacing between the cantilevered arms and the ground. A second spreading apparatus provides a fixed alignment of the spreading boom before, after, and during consecutive correction processes, in which the height of the spreading boom above the ground is readjusted according to a specified spacing between the cantilevered arms and the ground. A third spreading apparatus provides the spreading boom to be suspended passively and the passive suspension to be changeable at least with respect to one suspension property in order to effect a continuous change of alignment of the spreading boom. In this context, the continuous change is carried out slower than the self-stabilizing of the passive suspension.